This invention relates to a thermionic source of electrons for an electron gun, and more particularly to a one piece thermionic source of electrons with an aperture.
Electron guns are used to heat materials to produce vapors of the materials for deposition on an article. The electron gun typically includes an electron source, a focusing electrode, and an accelerating electrode. The electron source is typically a cathode heated by an electric current to cause the cathode to emit electrons. The focusing electrode is typically negatively charged to repel the electrons and thereby direct the electrons in a direction generally toward the accelerating electrode. The accelerating electrode is positioned downstream from the electron source and the focusing electrode. The accelerating electrode is typically less negatively charged than the electron source and the focusing electrode to cause the electrons to form into a beam and travel in the downstream direction.
One type of thermionic electron gun has a single elongated electron source having a ribbon shape. The ribbon shaped electrode is desirable for its simplicity and ease of use. However, many ions are produced as a result of the vaporization of the materials. Positively charged ions may be attracted to the negatively charged focusing electrode and thereby bombard and erode the electron source. The erosion has the effect of degrading the performance of the electron source and shortening its useful life.
U.S. Pat. No. 3,701,915 discloses an electron source that is less susceptible to bombardment by ions. The electron source is made up of two elongated emitters spaced apart and parallel to one another. Because of the focusing tendency of the focusing electrode, the ions do not strike the emitters but rather pass through the space between them and hit the focusing electrode. A substantial improvement in the life of the emitters is achieved. However, a two part electron source cannot be used on a gun designed for a single electron source unless the gun is modified. For example, a two part electron source requires means to electrically connect to and support the two emitters, as well as means to properly space the two emitters apart.
An object of the present invention is to provide an improved linear thermionic electron source that has a longer operating life than previous ribbon type linear thermionic electron sources yet does not require a two part electron source.
The present invention is predicated in part on the recognition that a ribbon type electron source can be one piece yet made less susceptible to ion bombardment and therefore longer operating, by providing an aperture in the electron source whereby ions do not strike the electron source but rather pass through the aperture.
According to the present invention, an apparatus for an electron gun includes a one piece thermionic electron source that extends in a longitudinal direction and has opposite end portions, an aperture disposed therebetween, and two longitudinal portions that extend in the longitudinal direction, are spaced apart from one another by the aperture and rigidly joined together by the opposite end portions.
In accordance with one detailed aspect of the invention, each of the emitter portions has a surface that is inclined toward that of the other.
The present invention provides an improved linear thermionic electron source that is less susceptible to ion bombardment and therefore has a longer operating life than previous ribbon type electron sources, yet does not have many of the disadvantages of an electron source with a dual emitter. Because the improved electron source is one piece, the source does not require support and relative positioning of multiple emitters such as that required by an electron source having two separate and parallel emitters. In addition, the one piece construction may make the electron source more rigid and thus more durable and less likely to deform than an electron source having two separate emitters.
These and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description, accompanying drawings, and claims.